Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models

We identified 17 magnetic clouds (MCs) with durations longer than 30 h, surveying the solar wind data obtained by the WIND and ACE spacecraft during 10 years from 1995 through 2004. Then, the magnetic field structures of these 17 MCs were analyzed by the technique of the least-squares fitting to...

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Main Authors: K. Marubashi, R. P. Lepping
Format: Article
Language:English
Published: Copernicus Publications 2007-11-01
Series:Annales Geophysicae
Online Access:https://www.ann-geophys.net/25/2453/2007/angeo-25-2453-2007.pdf
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spelling doaj-d720e56c265e45fb9a3a136672854d432020-11-24T23:38:33ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762007-11-01252453247710.5194/angeo-25-2453-2007Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope modelsK. Marubashi0K. Marubashi1R. P. Lepping2National Institute of Information and Communications Technology, Koganei, Tokyo 184-8795, Japannow at: Korea Astronomy and Space Science Institute, Daejeon 305–348, KoreaHeliophysics Science Division, NASA-Goddard Space Flight Center, Greenbelt, MD 20771, USAWe identified 17 magnetic clouds (MCs) with durations longer than 30 h, surveying the solar wind data obtained by the WIND and ACE spacecraft during 10 years from 1995 through 2004. Then, the magnetic field structures of these 17 MCs were analyzed by the technique of the least-squares fitting to force-free flux rope models. The analysis was made with both the cylinder and torus models when possible, and the results from the two models are compared. The torus model was used in order to approximate the curved portion of the MCs near the flanks of the MC loops. As a result, we classified the 17 MCs into 4 groups. They are (1) 5 MC events exhibiting magnetic field rotations through angles substantially larger than 180° which can be interpreted only by the torus model; (2) 3 other MC events that can be interpreted only by the torus model as well, though the rotation angles of magnetic fields are less than 180°; (3) 3 MC events for which similar geometries are obtained from both the torus and cylinder models; and (4) 6 MC events for which the resultant geometries obtained from both models are substantially different from each other, even though the observed magnetic field variations can be interpreted by either of the torus model or the cylinder model. It is concluded that the MC events in the first and second groups correspond to those cases where the spacecraft traversed the MCs near the flanks of the MC loops, the difference between the two being attributed to the difference in distance between the torus axis and the spacecraft trajectory. The MC events in the third group are interpreted as the cases where the spacecraft traversed near the apexes of the MC loops. For the MC events in the fourth group, the real geometry cannot be determined from the model fitting technique alone. Though an attempt was made to determine which model is more plausible for each of the MCs in this group by comparing the characteristics of associated bidirectional electron heat flows, the results were not very definitive. It was also found that the radii of the flux ropes obtained from the torus fitting tend to be generally smaller than those obtained from the cylinder fitting. This result raises a possible problem in estimating the magnetic flux and helicity carried away from the Sun by the MCs.https://www.ann-geophys.net/25/2453/2007/angeo-25-2453-2007.pdf
collection DOAJ
language English
format Article
sources DOAJ
author K. Marubashi
K. Marubashi
R. P. Lepping
spellingShingle K. Marubashi
K. Marubashi
R. P. Lepping
Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models
Annales Geophysicae
author_facet K. Marubashi
K. Marubashi
R. P. Lepping
author_sort K. Marubashi
title Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models
title_short Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models
title_full Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models
title_fullStr Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models
title_full_unstemmed Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models
title_sort long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models
publisher Copernicus Publications
series Annales Geophysicae
issn 0992-7689
1432-0576
publishDate 2007-11-01
description We identified 17 magnetic clouds (MCs) with durations longer than 30 h, surveying the solar wind data obtained by the WIND and ACE spacecraft during 10 years from 1995 through 2004. Then, the magnetic field structures of these 17 MCs were analyzed by the technique of the least-squares fitting to force-free flux rope models. The analysis was made with both the cylinder and torus models when possible, and the results from the two models are compared. The torus model was used in order to approximate the curved portion of the MCs near the flanks of the MC loops. As a result, we classified the 17 MCs into 4 groups. They are (1) 5 MC events exhibiting magnetic field rotations through angles substantially larger than 180° which can be interpreted only by the torus model; (2) 3 other MC events that can be interpreted only by the torus model as well, though the rotation angles of magnetic fields are less than 180°; (3) 3 MC events for which similar geometries are obtained from both the torus and cylinder models; and (4) 6 MC events for which the resultant geometries obtained from both models are substantially different from each other, even though the observed magnetic field variations can be interpreted by either of the torus model or the cylinder model. It is concluded that the MC events in the first and second groups correspond to those cases where the spacecraft traversed the MCs near the flanks of the MC loops, the difference between the two being attributed to the difference in distance between the torus axis and the spacecraft trajectory. The MC events in the third group are interpreted as the cases where the spacecraft traversed near the apexes of the MC loops. For the MC events in the fourth group, the real geometry cannot be determined from the model fitting technique alone. Though an attempt was made to determine which model is more plausible for each of the MCs in this group by comparing the characteristics of associated bidirectional electron heat flows, the results were not very definitive. It was also found that the radii of the flux ropes obtained from the torus fitting tend to be generally smaller than those obtained from the cylinder fitting. This result raises a possible problem in estimating the magnetic flux and helicity carried away from the Sun by the MCs.
url https://www.ann-geophys.net/25/2453/2007/angeo-25-2453-2007.pdf
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